1. Field of the Invention
This invention relates to a method of producing a rubber-resin composite structure, wherein a vulcanized rubber molding and a resin molding formed from a thermoplastic resin are adhesive bonded together at a high strength.
2. Description of the Related Art
Recently thermoplastic resins superior in mechanical strength, heat resistance, etc. such as engineering plastics or the like have been widely used as a metal substitute material, taking advantage of their characteristics and workability, and application fields of rubber-resin composites superseding rubber-metal composites are enlarging. For instance, with a rubber bushing used for an automobile suspension, etc. its outer cylinder surrounding a rubber elastomer is being changed from metal-made to a thermoplastic resin-made. Also in the fields of suspensions of machinery, vibration insulation or vibration damping components for architectures, a composite is used such that vulcanized rubber molding and resin molding of a high-rigidity resin material are united together.
These rubber-resin composites are generally produced by coating a chlorine-containing vulcanization adhesive agent to a surface of a thermoplastic resin molding and subsequently applying an unvulcanized rubber thereto, thus bonding by vulcanization. Accordingly, this process has various problems in that it necessitates a number of facilities at the vulcanization step, the heat of vulcanization affects the resin molding, and so on.
As a method applicable to the production of a rubber bushing fitted with an outer cylinder made of resin mentioned above, JP Patent Publication 1990-84310 A1 proposes such a process that comprises subjecting a surface of the vulcanized rubber molding to chlorination treatment, forming a vulcanization adhesive layer containing, as primary ingredients, resorcinol type phenol resin and aldehyde-modified polyvinyl alcohol on the chlorination-treated surface, arranging it in a mold cavity followed by injection molding of a thermoplastic resin under heating and melting condition. There, additional process is also proposed, which comprises forming a vulcanization adhesive layer containing chlorosulfonated polyethylene as a principal ingredient and injection molding a thermoplastic resin under heated and melted condition while heating the vulcanized rubber.
According to the method thus disclosed, a rubber-resin composite can be produced at a low cost without entailing deterioration in physical properties or deformation of thermoplastic resin due to heat history. Nevertheless this method runs into the difficulty that in producing a vibration-proof member for supporting a heavy-weight member such as automobile engine mount in a vibration-proof manner, sufficient mechanical strength cannot always be obtained. That is, for a vibration-proof rubber member exerted by high load, a thermoplastic resin is required to have a high mechanical strength to the extent that is not ruptured by the high load.
In view of the aforementioned problems, a principal object of this invention is to provide a method of producing a rubber-resin composite, wherein a vulcanized rubber molding and a thermoplastic resin molding are adhesive bonded together with a high adhesive strength, without causing deformation of the resin due to thermal history, while satisfying both moldability and mechanical strength.
This invention consists in a method of producing a rubber-resin composite composed of a vulcanized rubber molding and a thermoplastic resin molding adhesively bonded to it, which method comprises the sequential steps of (1) to (3):
(1) fashioning the vulcanized rubber molding by vulcanization molding;
(2) forming an adhesive layer containing as a primary component chlorosulfonated polyethylene on a surface of the vulcanized rubber molding to be bonded to the thermoplastic resin; and
(3), while arranging the vulcanized rubber molding in a mold, pouring a thermoplastic resin containing 30 to 60% by weight of inorganic short fiber under molten state into the mold thereby forming the thermoplastic molding and simultaneously adhesive-bonding the resin molding to the vulcanized rubber molding through the adhesive layer.
According to this invention, after the vulcanization adhesive layer containing primarily chlorosulfonated polyethylene is formed on the surface of the vulcanized rubber molding to which the resin is to be bonded, the thermoplastic resin is thus molded. Hence it is possible to produce the rubber-resin composite, whose vulcanized rubber and thermoplastic resin are bonded together at a high adhesive strength, without entailing deterioration in physical properties and deformation of the resin, at a low cost. Furthermore the thermoplastic resin contains 30 to 60% by weight of inorganic short fiber and consequently, it is possible to improve the mechanical strength of the resin molding without impairing the moldability.
In case where the inorganic short fiber is thus added to the thermoplastic resin to the extent that a sufficient reinforcement to the thermoplastic resin is exhibited, only by the adhesive layer containing as a principal ingredient chlorosulfonated polyethylene, there is a possibility that a sufficient adhesive strength between the rubber molding and the resin molding cannot be achieved. In that case, it is preferred to use the following procedures, either (a) or (b) below:
(a) a procedure of forming the adhesive agent layer by a composition obtained by adding a coupling agent to the adhesive agent containing as a primary ingredient chlorosulfonated polyethylene;
(b) a procedure of applying a coating solution containing a coupling agent to the surface of the adhesive layer after it is formed.
By adopting either of these procedures it is possible to enhance the adhesive strength to the vulcanized rubber molding to a sufficient degree from the practical viewpoint albeit the resin molding containing sufficient amount of inorganic short fiber for reinforcement purposes and to accomplish a stabilized adhesive strength.